In order to survey one, or in particular a plurality of target points, numerous geodetic survey apparatuses have been known since antiquity. As standard spatial data, distance and direction, or angle, from a measuring apparatus to the target point to be surveyed are in this case recorded and, in particular, the absolute position of the measuring apparatus is acquired together with possibly existing reference points.
Widely known examples of such geodetic survey apparatuses consist of the theodolite, tachymeter or total station, which is also referred to as an electronic tachymeter or computer tachymeter. A geodetic survey instrument of the prior art is described, for example, in the publication document EP 686 350. Such apparatuses have electrosensor angle and distance measurement functions, which allow determination of direction and distance to a selected target. The angle and distance quantities are in this case determined in the internal reference system of the apparatus and, for an absolute position determination, may possibly also need to be correlated with an external reference system.
In many geodetic applications, points are surveyed by placing specially configured target objects at them. These usually consist of a pole having a targetable marking or a reflector for defining the measurement distance, or the measurement point. Using a central geodetic survey apparatus, even a relatively large number of target objects can therefore be surveyed, although this requires that they be identified. In such survey tasks, in order to control the measurement process and establish or register measurement parameters, various data, instructions, words and other information need to be transmitted between the target object—in particular a handholdable data acquisition apparatus at the target object—and the central measuring apparatus. Examples of such data are the identification of the target object, inclination of the pole, height of the reflector above ground, reflector constants or measurement values such as temperature or air pressure.
Modern total stations have microprocessors for the digital postprocessing and storage of acquired measurement data. The apparatuses are generally produced in a compact and integrated design, usually with coaxial distance and angle measurement elements as well as calculation, control and storage units integrated in an apparatus. Depending on the development level of the total station, means for motorizing the target optics, for reflectorless distance measurement, for automatic target search and tracking and for remote control of the entire apparatus are integrated. Total stations known from the prior art furthermore have a radio data interface for setting up a radio link to external peripheral components, for example to a data acquisition apparatus which, in particular, may be formed as a handholdable data logger, remote control unit, array processor, notebook, small computer or PDA. By means of the data interface, measurement data acquired and stored by the total station can be output to external postprocessing, externally acquired measurement data can be read into the total station for storage and/or postprocessing, remote control signals for remote control of the total station or of another external component, particularly in mobile field use, can be input or output, and control software can be transferred into the total station.
For sighting or targeting the target point to be surveyed, geodetic survey apparatuses according to the generic type comprise, for example, a target telescope, for example an optical telescope, as a sighting device. The target telescope can generally be rotated about a vertical axis and about a horizontal tilt axis relative to a base of the measuring apparatus, so that the telescope can be oriented towards the point to be surveyed by swiveling and tilting. In addition to the optical viewing channel, modern apparatuses may have a camera integrated in the target telescope, and for example oriented coaxially or parallel, for acquiring an image, in which case the acquired image may in particular be represented as a live image on the display of the display/control unit and/or on a display of the peripheral apparatus used for the remote control—for example of the data logger or the remote control unit. The optics of the sighting device may in this case have a manual focus—for example an adjustment screw for changing the position of focusing optics—or an autofocus, the focal position being changed for example by servo motors. Automatic focusing devices for target telescopes of geodetic apparatuses are known, for example, from DE 197 107 22, DE 199 267 06 or DE 199 495 80.
The sighting of a target reflector may in this case be carried out in particular by means of a live image, which is displayed to the user in the display of the data logger or of the remote control unit, which is provided by a camera—for example arranged coaxially in the target telescope or with an orientation parallel to the target telescope—as the sighting device of the total station. Accordingly, the user can orientate the total station with the aid of the live image in accordance with the desired target identifiable in the live image.
EP 1 734 336 discloses a survey system comprising a target unit, which has a reflector and an optical receiver and transmitter. It is in this case proposed to use the optical transmitter of the target unit inter alia to assist the automatic target search process. Thus, after reception of the search or measurement radiation, the target object can communicate its own identification, for example the reflector number or the reflector type, back to the survey station with the aid of the transmitter of the target unit. The survey station can therefore identify the target object found and be configured optimally with respect to the target object.
EP 1 573 271 discloses a target unit also having an optical transmitter, wherein—after reception of measurement radiation of a survey apparatus—the target unit sends back an optical signal on which the target unit's own identity is modulated.
A feature common to the aforementioned survey systems from the prior art is that, optionally with the use of a camera, the target unit or a survey stick provided with the target unit is sighted or observed by a stationary position determination unit, for example a total station. However, no automated guidance of an operator by using the image data recorded by the stationary position determination unit for an intended target point for the purpose of defining the latter is disclosed, so that the definition process is relatively laborious for an operator and entails considerable time expenditure when accurate definition of the target point is intended to be ensured.
For a solution to this problem, U.S. Pat. No. 7,222,021 and the corresponding EP 1 293 755 propose a survey system, referred to in this patent as an operator guiding system, having a stationary base station corresponding to a stationary position determination unit, which is equipped with imaging means, for example a camera, and a mobile station with the function of a mobile target unit, which is equipped with display means, for example a display for representing a current position of the user on the basis of stored landscape images or data, and current images, as seen from the stationary measurement unit. They also disclose the way in which an operator can be guided to the target point by means of correlation between the position data currently measured from the stationary measurement station, including a camera image, for the mobile station, and stored data comprising the intended position of the target point, by marking on the display of the target unit, for example by a direction display by means of an arrow on the display.
Although the process of defining a target point can be accelerated with this system described in U.S. Pat. No. 7,222,021 and the corresponding EP 1 293 755, the disclosure does not reveal any possibilities of improving the accuracy of the definition of the target point; this is because the mobile station does not have its own image acquisition means, and real images are acquired only by the distant stationary total station, while merely synthetic calculated representations from a bird's-eye perspective are used on a mobile display for guiding the mobile station, for example a pole with a reflector.
WO 2010/080950 essentially discloses a pole having a camera fitted (according to the figures) on the upper end in order to determine an azimuth for a target point. It is to be noted that this positioning of the camera can restrict the operability of the apparatus by a user shadowing the image. Connection to a theodolite or a total station is mentioned, but without disclosure regarding coordination/correlation of image data. This document contains no mention of the use of an effect of the fitted camera, or the data thereof, on possible precise positioning of the pole on a target point.